Chevrolet 70 1969 Series, Shop Manual

Page: 219 / 913

BRAKES
5B-26
used in city "stop and start" driving will require
different service operations and intervals than one
hauling "over the road" for long distance. With this
in mind, all service intervals should be related to a
specific vehicle.
Compression and subsequent cooling of air
causes the moisture in the air to condense. This
moisture collects in air tank and should be drained
daily. Drain cocks are provided at bottom of air
tanks for this purpose. Satisfactory draining is
accomplished only by leaving the drain cocks open
after compressed air has escaped and until all
drainage stops.
Some vehicles are equipped with a moisture
ejector valve (optional), which eliminates the need
for daily drainage of air tanks. For description of
how this valve works, refer to procedures under
heading of "Moisture Ejector Valve."
The complete air system should be checked
for leakage at regular intervals. Build up air pres­
sure in system to governor cut-out point (100-111
psi), then with engine stopped and brakes released,
observe rate of air pressure drop registered by
the dash air pressure gauge. The rate of drop
should not exceed two pounds per minute. With
engine stopped and brakes fully applied, observe
rate of air pressure drop registered by the dash
gauge. Rate of drop should not exceed three pounds
per minute. If leakage is excessive, leakage test
should be made at air line connections and at all
air brake control units as directed under individual
headings later in this section.
In cold weather, particular attention should be
given to draining of moisture from air system.
BRAKE ADJUSTMENTS
Brake adjustments to compensate for normal
lining wear are made at slack adjuster at each
wheel. Adjustment must be made before the brake
chamber push rod travel reaches the maximum
working stroke.
Line to Air Gauge
Valve Mounting Bolt
and Nut (in Engine
Compartment)
Lines to Trailer
Brakes Hand Control
Valve
9 Application
Double Check Valve
and Stop Light Switch
5 Line to Tractor
Protection Valve
6
Pedal Stop Button
7 Pedal Assembly
8 Pedal to Valve Bolts
Valve Assembly T-2126
Figure 2 — Brake Pedal a nd Application Valve
Installed (ConventionalI f Typical)
P E D A L STOP S C R E W A D J U S T M E N T
(C O N V E N T IO N A L M O D E L S - Fig. 2)
On all conventional models, both Midi and-Ross
and Bendix-Westinghouse application valves (pedal
assembly included) are used. Midland-Ross has a
stop screw and Bendix-Westinghouse has a stop
button as part of the assembly. This stop screw,
or button, is used to adjust pedal to provide proper
pedal travel. If travel is too great, application will
be too slow and full applic ation may not be obtained.
If travel is not great enough, brakes may not re­
lease completely. Adjust stop screw (button) as
follows:
1. Loosen lock nut.
2. Turn stop screw (M-R) into pedal bracket
until pedal roller does not touch exposed end of
valve piston; or (B-W) until plunger does not touch
valve piston.
3. Turn stop screw (M-R) out of pedal bracket
until roller 'JUST T O U C H E S exposed end of valve
piston; or (B-W) until plunger JU S T T O U C H E S
valve piston. In other words, there should be N O
F R E E P L A Y between pedal and valve piston.
4. Tighten lock nut without moving stop screw
(or button).
5. Check brake operation for full application
and release.
P E D A L STOP S C R E W A D J U S T M E N T
(T IL T CAB M O D E L S - Fig. 3)
Pedal stop screw adjustment controls the ex­
haust opening between the hollow end of the appli­
cation valve piston and the exhaust valve. It also
controls the pedal travel before brake application
begins. If stop screw is turned down toofar, it will
prevent the piston from leaving the exhaust valve
and brakes will not release. If it does not open far
CHEVROLET SERIES 70 -80 H EAVY DUTY TRUCK SH O P M A N U A L